I really don't think the Spurs will turn into their 2008 selves just because they got Wemby. Wemby is not Duncan. He's not likely to be an MVP out-of-the-box player. He might bust. If it made sense to go for potential before the lottery, it makes sense now.
I also hope and believe that the Spurs don't think about development in this way. Yes, some guys are more finished than others. Upside is a real thing. But it's not the case that players with higher upside have to have lower floors. Kawhi is a HoFer with a extremely high floor who went in the middle of the round. The Spurs screwed the pooch with Primo, but both Vassell and Sochan were players who had seemingly useful floors but who still show a lot of upside. I would liken Ausar in that boat, since his defensive ability and athleticism should translate. Even so, I don't think the Spurs should look at players like they're scratch-off tickets. There's not a "30 percent chance Player X lives up to his potential". That logic is made up. Instead, there's a roadmap a given player has to develop skills and physical traits to improve, and a team has to factor in both the player's willingness to put in the work and their own ability to provide the instruction and resources for the player to move along that roadmap.
So it's okay if the Spurs pass on Amen because they don't think they can fix his shot. It's okay if they think Black can provide them more value than Ausar. Those are definitely the types of considerations that go into a draft board. But they're not actually quantifiable conditions, and trying to put a number to them in a desire to add an air of objectivity doesn't all of the sudden make real people behave like a RNGs. If the Spurs thought they and a prospect could work together on a roadmap that would make that player a useful asset to their team before they won the lottery, they shouldn't all of the sudden not believe that.
Ultimately, all of these evaluations fit into the wider concept of BPA, and most of the factors shouldn't be any different now. There are examples for the opposite, sure. Drafting a player like Wemby can definitely alter the board given that they'd be taking a guy at a position where they already took a player last year. Trading up for yet another PF would be weird (so like downgrading Miller totally makes sense even if he might be downgraded a bit too much). But if there are players that the Spurs would've felt comfortable taking at three or later, they should still have the same grade, and most of them should still be right where they were on the board.